1. Field of the Invention
The present invention relates to an electret loudspeaker device. More particularly, the present invention relates to a material of an electret diaphragm for an electret loudspeaker device and the fabrication method thereof.
2. Description of Related Art
The electret loudspeaker device operates in a vibrating mode of the electret diaphragm to produce the sound, by varying the electrostatic force of the electret diaphragm and through interaction between the applied voltage from the acoustic waves and electric charges of the electret diaphragm. One of the commonly used materials for the electret diaphragm may be expanded polytetrafluoroethylene (ePTFE) material, for example. The ePTFE membrane is a porous membrane formed by unidirectionally mechanical stretched polytetrafluoroethylene (PTFE), which is white, flexible and tensile and has a meshed structure formed from connected minute fibers and with numerous pores. Based on research studies, the high contact area of these pores allows the ePTFE membrane to store more electric charges and have higher electret property. However, the electret property of the ePTFE electret diaphragm swiftly decreased when encountering environmental humidity or high temperature, which significantly deteriorates the sound generating capability of the electret loudspeaker device. Hence, the stability of the electret loudspeaker device using the ePTFE electret diaphragm turns out to be unacceptable. Accordingly, it is desirable to develop the electret loudspeaker device tolerant to humidity and high temperature.